Oh the fun you could have with this one. I doubt the Nigerians would be anything close to eager to report you to the FBI if you happened to represent yourself as an FBI Special Agent. Perhaps Special Agent Mulder should email them back?
Nah, I cant impersonate an FBI agent. The FBI would take a dim view of that. I once provided one of them with a phone number to the FBI office, telling them that was my contact number. Apparently they actually called it, and then later emailed me, complaining “why did you give me the number to the FBI?”